Digital documents and images (herein images) typically exist in the digital realm as a formatted file including a bitmap of pixels. The images may be represented in a particular format and may include color images represented in a particular color space and format, grayscale images and monochrome images. In the case of vector based image representations, such representations could be converted to bitmap representation.
There are many known issues and concerns regarding accuracy in transforming a digital image to a physical image using a particular output device such as a printer and a particular medium such as paper, particularly with regard to color matching. Furthermore, it may be desirable to convert a physical image to a digital form using an image capture or scanning device (herein scanner). Similarly, there are concerns regarding accuracy of such transformation from a physical image to a digital image. For example, physical effects of the printing process that distort the output of the printing process vary by printing technology but include ink bleeding for inkjet printing systems and thermal heating effects for thermal printing systems. Similarly, physical effects associated with scanning distort the physical to digital transformation including scanning resolution limitations (particularly in scanning continuous analog images), scanning grid mismatch (for scanning digital pixels) and color mismatch for color images.
In order to predict the effects of such physical transformations for a particular digital image, printer and scanner, print-scan models may be developed to predict the resulting distortion. In some cases, devices such as thermal printers may modify the next print row in local memory before printing it to compensate for thermal heating effects. Scanner manufactures may provide adjustable software controls to deal with effects such as gamma correction. Image enhancement features included by printer and scanner manufacturers generally aim to improve the appearance of the image to the human visual system, rather than to increase the accuracy of the transformation of the image from digital to analog form and back to digital.
In the area of copy detection for physical documents, systems are known including copy detection patterns (CDPs) that may be placed in a particular region of a document reserved for the purpose. Furthermore, several copy detection systems are known that utilize visible and invisible digital watermarks (fragile and/or robust) that are applied to an image. Commercially available systems include those available from Digimarc Corporation of Beaverton, Oreg. and Mediasec Technologies, LLC of Providence, R.I. Print-scan models may be useful in watermarking verification systems in predicting what a recovered watermark should look like after passing through one or more print-scan processes or copy generations. A system for utilizing print-scan compensation in a watermarking method is described in commonly-owned, co-pending patent application Ser. No. 10/720,503, filed Nov. 23, 2003 entitled Watermarking Method With Print-Scan Compensation, which is incorporated herein by reference. A system using printer and scanner characteristics is show in U.S. Pat. No. 6,947,179 B1, issued Sep. 20, 2005 to Cordery, et al., entitled Method for determining the information capacity of a paper channel and for designing or selecting a set of bitmaps representative of symbols to be printed on said channel.
Traditional print-scan simulation models attempt to balance many effects of the physical print-scan process in an attempt to predict the resulting physical transformations. However, such models are typically not completely accurate, because they approximate the print-scan process and often produce predictions that are not very accurate. Furthermore, there are no known print-scan modeling systems for modeling a system that uses the same types of printers and scanners to process a particular category of images that have similar histograms. Additionally, traditional histogram matching processes are computationally difficult and not very accurate.
Accordingly, there is a need for a print-scan simulation modeling process and model for providing more accurate print scan models and simulations. Additionally, there is a need for a print-scan simulation modeling process and model for providing more accurate print scan models and simulations for systems using same types of printers and scanners to process a particular category of images that have similar histograms. Furthermore, there is a need for a print-scan simulation modeling process and model for providing histogram constrained print-scan models using a computationally efficient process.